What: Shares of rail company Kansas City Southern (NYSE:KSU) jumped as much as 12% in early trading on Wall Street after the company reported fourth-quarter earnings. By noon, shares had settled lower to a 5% gain on the day.

So what: Revenue dropped 7% last quarter to $598 million and net income dropped 1% to $139.3 million, or $1.28 per share. The revenue figure fell short of analysts' expectation of $609.1 million but earnings adjusted for one-time items of $1.23 per share easily topped estimates of $1.10.

Now what: Management has done a good job of lowering costs, with operating expenses down 12% from a year ago. That helped offset a 2% decline in carload volumes, which is the driver of revenue. Despite the stronger-than-expected results, there are still some major uncertainties in 2016. Metals and scrap volume plunged 25% in the fourth quarter and there's no sign that's going to pick up in the near term. Petroleum was also a strength, growing 20% year over year, but that'll likely slow as U.S. oil production falls.

Given the uncertainty and the declining revenues, I wouldn't look at this earnings beat as a reason to buy. Shares are still fairly expensive at 15 times earnings and that could prove expensive if volumes fall further in 2016.